Mucopolysaccharidoses (MPSs) are degenerative genetic diseases linked to an enzymatic defect. In particular, MPSs are caused by the deficiency or the inactivity of lysosomal enzymes which catalyze the gradual metabolism of complex sugar molecules called glycosaminoglycans (GAGs). These enzymatic deficiencies cause an accumulation of GAGs in the cells, the tissues and, in particular, the cell lysosomes of affected subjects, leading to permanent and progressive cell damage which affects the appearance, the physical capacities, the organ function and, in most cases, the mental development of affected subjects.
Eleven distinct enzymatic defects have been identified, corresponding to seven distinct clinical categories of MPS. Each MPS is characterized by a deficiency or inactivity of one or more enzymes which degrade mucopolysaccharides, namely heparan sulfate, dermatan sulfate, chondroitin sulfate and keratan sulfate.
MPS I is divided into three subtypes based on severity of symptoms. All three types result from an absence of, or insufficient levels of, the enzyme alpha-L-iduronidase.
Children born to an MPS I parent carry the defective gene.
MPS I H (also called Hurler syndrome or α-L-iduronidase deficiency), is the most severe of the MPS I subtypes. Developmental delay is evident by the end of the first year, and patients usually stop developing between ages 2 and 4. This is followed by progressive mental decline and loss of physical skills. Language may be limited due to hearing loss and an enlarged tongue. In time, the clear layers of the cornea become clouded and retinas may begin to degenerate. Carpal tunnel syndrome (or similar compression of nerves elsewhere in the body) and restricted joint movement are common. Affected children may be quite large at birth and appear normal but may have inguinal (in the groin) or umbilical (where the umbilical cord passes through the abdomen) hernias. Growth in height may be faster than normal but begins to slow before the end of the first year and often ends around age 3. Many children develop a short body trunk and a maximum stature of less than 4 feet. Distinct facial features (including flat face, depressed nasal bridge, and bulging forehead) become more evident in the second year. By age 2, the ribs have widened and are oar-shaped. The liver, spleen, and heart are often enlarged. Children may experience noisy breathing and recurring upper respiratory tract and ear infections. Feeding may be difficult for some children, and many experience periodic bowel problems. Children with Hurler syndrome often die before age 10 from obstructive airway disease, respiratory infections, and cardiac complications.
MPS I S, Scheie syndrome, is the mildest form of MPS 1. Symptoms generally begin to appear after age 5, with diagnosis most commonly made after age 10. Children with Scheie syndrome have normal intelligence or may have mild learning disabilities; some may have psychiatric problems. Glaucoma, retinal degeneration, and clouded corneas may significantly impair vision. Other problems include carpal tunnel syndrome or other nerve compression, stiff joints, claw hands and deformed feet, a short neck, and aortic valve disease. Some affected individuals also have obstructive airway disease and sleep apnea. Persons with Scheie syndrome can live into adulthood.
MPS I H-S, Hurler-Scheie syndrome, is less severe than Hurler syndrome alone. Symptoms generally begin between ages 3 and 8. Children may have moderate intellectual disability and learning difficulties. Skeletal and systemic irregularities include short stature, marked smallness in the jaws, progressive joint stiffness, compressed spinal cord, clouded corneas, hearing loss, heart disease, coarse facial features, and umbilical hernia. Respiratory problems, sleep apnea, and heart disease may develop in adolescence. Some persons with MPS I H-S need continuous positive airway pressure during sleep to ease breathing. Life expectancy is generally into the late teens or early twenties.
MPS II, also known as Hunter syndrome, is caused by lack of the enzyme iduronate sulfatase. Hunter syndrome has two clinical subtypes and (since it shows X-linked recessive inheritance) is the only one of the mucopolysaccharidoses in which the mother alone can pass the defective gene to a son. The incidence of Hunter syndrome is estimated to be 1 in 100,000 to 150,000 male births.
Mucopolysaccharidosis type VI (MPS VI) or Maroteaux-Lamy disease is a lysosomal storage disease, of the mucopolysaccharidosis group, characterized by severe somatic involvement and an absence of psycho-intellectual regression. The prevalence of this rare mucopolysaccharidosis is between 1/250 000 and 1/600 000 births. In the severe forms, the first clinical manifestations occur between 6 and 24 months and are gradually accentuated: facial dysmorphia (macroglossia, mouth constantly half open, thick features), joint limitations, very severe dysostosis multiplex (platyspondyly, kyphosis, scoliosis, pectus carinatum, genu valgum, long bone deformation), small size (less than 1.10 m), hepatomegaly, heart valve damage, cardiomyopathy, deafness, corneal opacities. Intellectual development is usually normal or virtually normal, but the auditory and ophthalmological damage can cause learning difficulties. The symptoms and the severity of the disease vary considerably from one patient to the other and intermediate forms, or even very moderate forms also exist (spondyloepiphyseal-metaphyseal dysplasia associated with cardiovascular involvement). Like the other mucopolysaccharidoses, Maroteaux-Lamy disease is linked to the defect of an enzyme of mucopolysaccharide metabolism, in the case in point N-acetylgalactosamine-4-sulfatase (also called arylsulfatase B). This enzyme metabolizes the sulfate group of dermatan sulfate (Neufeld et al.: “The mucopolysaccharidoses” The Metabolic Basis of Inherited Diseases, eds. Scriver et al, New York, McGraw-Hill, 1989, p. 1565-1587). This enzymatic defect blocks the gradual degradation of dermatan sulfate, thereby leading to an accumulation of dermatan sulfate in the lysosomes of the storage tissues. At the current time, there is just one medicament authorized for the treatment of this disease: Naglazyme® (recombinant human galsulfase), the cost of which is extremely high (in the United States, it is about $ 350 000 per year). An alternative to this treatment is bone marrow allograft.
Mucopolysaccharidosis type VII (MPS VII) or Sly disease is a very rare lysosomal storage disease of the mucopolysaccharidosis group. The symptomology is extremely heterogeneous: antenatal forms (nonimmune fetoplacental anasarca), severe neonatal forms (with dysmorphia, hernias, hepatosplenomegaly, club feet, dysostosis, significant hypotonia and neurological problems evolving to retarded growth and a profound intellectual deficiency in the event of survival) and very moderate forms discovered at adolescence or even at adult age (thoracic kyphosis). The disease is due to a defect in beta-D-glucuronidase, responsible for accumulation, in the lysosomes, of various glycosaminoglycans: dermatan sulfate, heparan sulfate and chondroitin sulfate. There is at the current time no effective treatment for this disease.
There is therefore clearly a need to provide subjects suffering from MPS type I, II, VI and VII with a drug treatment, and in the case of MPS type VI, an alternative treatment not derived from biotechnology.
Odiparcil (4-methyl-2-oxo-2H-1-benzopyran-7-yl-5-thio-β-D-xylopyranoside; CAS 137215-12-4) belongs to the thioxyloside family. This compound, described in patent application EP-A-0 421 829, corresponds to the formula:

This compound was the subject of a clinical development (phases 1 and 2) in the treatment of thrombosis at the end of the 1990s and at the beginning of the 2000s. Its mechanism of action can be summarized in the following way: Odiparcil behaves as a substrate for an enzyme, GT1 (galactosyl transferase 1), which initiates the synthesis of GAG chains toward the dermatan sulfate/chondroitin sulfate pathway. These GAGs are cell constituents as proteoglycans, where they are linked to the core-protein moiety at serine residues through a linkage region composed of xylose-galactose-galactose. Proteoglycans are widely distributed in tissues, especially connective tissues, are major constituents of cell membranes and cell extracellular matrix. They have varied biological roles, ranging from the control of coagulation (heparin/heparan and dermatan sulfate secreted into the circulation), structural and physical organisation of cartilages to the regulation of growth factors (beta-glycan).
It has now been noted, and this is the subject of the present invention, that odiparcil makes it possible to increase total GAG synthesis at the extracellular level and, by the same token, will contribute to reducing the intracellular GAG load by acting as a “decoy” making the residual activity of N-acetylgalactosamine-4-sulfatase more effective. It is thus possible to envision the treatment of MPS type I, II, VI and VII owing to the decrease in GAG accumulation at the intracellular level.